Help with my hot (And not in a good way) VY V6

[Antsmash]

I'm after your guys wise wisdom once again.

I' had to replace my heater tap a few months ago and have had cooling problem ever since. Found the cooling system to be in horrible condition and start replacing. This is what I (And mechanic) have done, in order.

Replace heater tap
3 Flushes (Started overheating at lights)
Replaced Radiator Cap
Replaced Hoses
Replace Water pump
Replaced Thermostat
Replaced Radiator

Now it has been going fairly well after the new radiator (Apparently it was really blocked and was still the original after 250,000k).

BUT

I have noticed driving around tight town streets and sitting at lights it sometimes pops above half, then drops back under usually 5 seconds after I set off.

I have notice two things.
1) I have never seen the low speed fan spin. I tried the trick when you unplug the temp sensor and start car. This started the high speed fan
okay but not the low. I today just replaced the relay, this hasn't helped. Is there an easy way to put 12v to the low speed fan?

2) I stopped yesterday for 5min and could hear the coolant in the overflow tank boiling as it came out of the overflow hose. And continued to
boil for the whole 5min.

Any ideas would be appreciated. I have got another radiator cap today from Holden just incase.

Cheers.

 

[Dr HaxZaw]

could be an issue with the computer or temp sender which is why its not turning the low speed on

 

[bsm]

Does the temp go up with aircon on?

Did you change coolant switch?

The coolant switch controls the thermo fans if aircon is on it bybasses the switch, or if you unplug the coolant switch it should automatic trip thermo fans as a fail safe.

 

[Antsmash]

Does the temp go up with aircon on?

Did you change coolant switch?

The coolant switch controls the thermo fans if aircon is on it bybasses the switch, or if you unplug the coolant switch it should automatic trip thermo fans as a fail safe.

Hey I always have the aircon on anyway to keep high fan on when possible

Nope I haven't check the switch? Where is it?

 

[wortus]

take out the low speed fan relay, 2 of the contacts in the socket correspond to the normally open contacts of th erelay. One of these should have +12Volts on it. Bridge them out and the fan should run.
There is probably a diagram of the relay pin configuration on the side of it.